Rotaxane Wraps

Organic polymers that conduct electricity--materials recognized by this year's recentNobel Prize in Chemistry--hold tremendous promise. For applications in a number of electronic devices and circuits, they could prove cheaper, lighter and sturdier than traditional semiconductors. When used as wires, though, they might need insulation to guard against crosstalk; when exposed to air, they degrade. Now, however, Harry Anderson and his colleagues at the University of Oxford have described a way to wrap these plastic wires, threading tubes onto them to form molecules called rotaxanes (illustration at right shows an example of a rotaxane). Their paper appears in the October issue of the journal Angewandte Chemie.

So-called polyrotaxanes, first made in the early 1990s by Akira Harada and his colleagues at Osaka University, are reminiscent of a string of beads. A doughnut-shaped molecule wraps around a molecular chain, knotted by bulky chemical groups on either end. Forces between the beads and string help thread the two together. Anderson's group succeeded in wrapping the majority of a polymer string with sugar-based cyclodextrin beads. And rather than creating the string first and then threading on the beads, they assembled the complex all at once. The wrap did not seem to alter the way the polymer absorbs light, and so they are hopeful that its electrical properties remained intact. Further tests will establish whether the wrap insulates the polymer as expected.